The supremacy held by the merchant marine of the United States in 1851 was maintained until about 1856, and during this period American ships continued to be built, bought, and chartered by British ship-owners; but after the great financial depression which affected both countries from 1857 to 1859, British ship-owners no longer needed American-built ships, for in Great Britain iron had by this time superseded wood in the construction of large vessels. Thus the advantage to the United States of having an abundant supply of timber was taken away, while the advantage of Free Trade, with low cost of living, was on the side of England. Moreover, the spirit of enterprise, which had been growing in Great Britain during the years of free competition in the carrying trade since 1849, was having its effect. Following the repeal of the Navigation Laws, the Merchant Shipping Act of 1854, a wise and far-seeing measure, completed the foundation upon which the merchant marine of Great Britain has been developed. This act of Parliament contains 548 clauses, dealing with all questions which relate to British merchant ships and seamen, including tonnage. The ship-builders of Great Britain had been much hampered by the old tonnage laws and were glad to see them abolished.[16] The new tonnage rules, which are still in force, were based upon the actual cubic capacity of the hull, the unit of 100 cubic feet being one ton register, so that a vessel measuring 100,000 cubic feet internal capacity registers 1000 tons, and is able to carry 2000 tons at 50 cubic feet per ton. This new system of measurement encouraged the application of scientific knowledge to the design of vessels, and, as we shall see, helped somewhat to prolong the clipper ship era in England, when it was practically dead in the United States. It is true that during our Civil War American ships were still sold in England, but this was rather because their owners had no profitable use for them at home than from any lack of British iron vessels. Since that period, the decline of American shipping, for reasons that should be well understood, has been constant.